linusdm / live_tcp

Experimenting with elixir, GenServers and gen_tcp

LiveTcp

This is an experiment to monitor a TCP service that only exposes a request/response inteface without a durable socket connection. Any observed changes are broadcast over a Phoenix PubSub to allow LiveViews to subscribe to these changes.

Apps

This umbrella project contains two apps:

• :live_tcp_monitor a simple Phoenix application that starts and consumes the monitors.
• :live_tcp_server a simple TCP server to emulate a back-end. It also exposes an API through iex to change values.

Both applications are started when you run iex -S phx.server from the root folder.

TODO

• Start a very simple embedded TCP server and add an interface to change values (from iex).
• Dynamically start monitors.
• Observe changes in a LiveView.
• Persist monitor specifications to survive a system restart, and make sure all registered monitors are restarted at startup.
• Use Ranch to implement the TCP server.
• Do a performance benchmark with a few thousand monitors.

Development

You can use asdf and the provided .tool-versions to get the correct erlang and elixir environment.

Start up a postgres database with docker by running docker-compose up -d in the root folder. Stop the database by running docker-compose down --remove-orphans.

Alternatively you can use following commands to start and stop a postgres database, using only docker without docker-compose:

docker run --detach -e POSTGRES_PASSWORD="postgres" -p 5432:5432 --name live_tcp_db postgres
docker stop live_tcp_db && docker rm live_tcp_db

To start your Phoenix server:

• Install dependencies with mix deps.get (in the root folder)
• Create and migrate your database with mix ecto.setup (in the apps/live_tcp_monitor folder)
• Start Phoenix endpoint with mix phx.server or inside IEx with iex -S mix phx.server (do this in the root folder to make sure both applications start)

Now you can visit localhost:4000 from your browser.

Use the application

To start a monitor with some identifier simply visit localhost:4000/monitors/1 (the last part inidicates the identifier).

To change a monitored value you need the iex console. Simply execute:

LiveTcp.Server.set_value("1", "new value")

The first arguement indicates the identifier (which you used to start the monitor above). The second argument is the new value for this identifier. This change should be observed within a few seconds, without reloading the LiveView.